Alaganandan Nanthakumar

Copper-dioxygen chemistry and modeling the Fe-Cu center in cytochrome c oxidase

The copper(1) complex [(TMPA)Cu(RCN)]+ (1) binds 02 forming [{ (TMPA)Cu}2(02)]2+ (2), with trans-y-1, 2 peroxo-coordination. Ligands with quinolyl groups substituting for the pyridyl donors in TMPA cause dramatic changes in the course of reaction, in one case stabilizing a CdO2 1:l adduct [(BQPA)Cu(02)]+ (6). The kinetics/thermodynamics are compared. Reaction of 1 with (F 8-TPP)Fe(II)pip2 (8) and 02 yields the p-0x0 species [(Fg-TPP)Fem-O-Cun(TMPA)]+ (9); this reversibly protonates giving p-hydroxo bridged [(Fg-TPP)Fe-(OH)-Cu(TMPA)]2+ (12). The novel NMR properties of 9 are described. These complexes are discussed in terms of their model 02-chemistry in hemocyanins or cytochrome c oxidase.

Copper–dioxygen reactivity involved in the formation of µ-oxo [(por)FeIII–O–CuIIL]+ heterodinuclear complexes (por = porphyrinate, L = tetradentate ligand), and novel synthesis of square-planar FeII(por) species

In the reaction of FeIII(por) species with [LCuI(KMeCN)]+ and O2 to give µ-oxo [(por)FeIII–O–CuIIL]+3(por = porphyrinate, L = tetradentate ligand), copper–dioxygen adducts or their decomposition products must be present, otherwise [(por)FeIII–OH] or [(por)FeIII–O–FeIII(por)] products appear; a novel synthesis ot square-planar FeII(por) is also described.

Dioxygen Reactivity Models for Cytochrome C Oxidase: Synthesis and Characterization of Oxo and Hydroxo-Bridged Porphyrin-Iron/Copper Dinuclear Complexes

The synthesis of appropriate transition-metal complexes to model the structural, spectroscopic, and magnetic properties of a metalloprotein active-site provides an opportunity to consider the function and associated mechanism of that metalloprotein at the molecular level. One nice example is the dinuclear cuprous amine-bis-pyridyl complex, which effects arene hydroxylation (albeit of the ligand m-xylyl spacer) using molecular oxygen (O2).1 This extraordinary reaction involves cleavage of the O-O bond and subsequent insertion of an oxygen atom into an arene C-H bond under essentially ambient conditions, to model the function of copper monooxygenases such as tyrosinase. Another excellent example is the generation of dicupric trans-µ-1,2-peroxo complexes from cuprous precursors and O2, reversibly,2–4 to model the oxygen-transport property of the protein hemocyanin, which subsequently was discovered to bind O2 in η2:η2 fashion, as shown in Figure 1.4 The metalloprotein cytochrome c oxidase,5 however, due to its combination of diverse and unusual active-site metal centers, has eluded a convincing model description. As for its function, it probably binds O2 at a dinuclear site comprising heme-iron and histidyl-copper coordination; it then cleaves the O-O bond, via reduction, (vide infra ).5 The structural changes associated with this dinuclear site during turnover, and the intermediates produced therefrom, are by no means clearly understood. In the resting state, the dinuclear site exhibits strong antiferromagnetic coupling (-J =200 cm-1) suggesting the involvement of a bridging ligand, often postulated as µ-sulfido, µ-chloro, or µ-hydroxo. Thus, we have endeavored to synthesize model complexes of this enigmatic dinuclear site.